The present invention provides a low cost preparation of ultra-low CTE and low dielectric loss high temperature co-fired ceramic (HTCC) substrates for highly integrated monolithic millimeter-wave integrated circuits (MMICs) utilized in high temperature environment. This HTCC zircon substrate is advantageous over currently available HTCC substrates in terms of cost effectiveness, excellent dielectric properties, close to zero thermal expansively, high thermal conductivity and good mechanical properties.